Phonograph recorder and reproducer arm



July 5, 1932. L A. ELMER PHONOGRAPH RECORDER AND REPRODUCER ARM Filed July 22, 1931 AAA INVENTOR L.A.ELMER. WW

ATTORNEY v Patented July 5, 1932 UNITED STATES PATENT OFFICE LLOYD A. ZELMER, OF WEST ORANGE, NIIEHV JERSEY, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, 015 NEW YORK, N. Y A CORPORATION OF NEW YORK PEONOGBAPE RECORDED AN D REPBODUOER ABM Application filed July 22, 1931. Serial fie. 552,371.

.6: from disc records are often impaired by the effects of extraneous vlbrations and forces imparted to the stylus of the translating device either through the groove itself or through the reproducer arm support. When the reproducer armis in any position other than the tangent position with respect to its cooperating groove the force of friction be tween the stylus and groove has a lateral as well as a longitudinal component which tends to turn the arm toward the tangent or neutral position. This has also been found to be a contributing factor to the discontmu ty of reproduction, since very little force is required in addition to the lateral component to cause the stylus to leave its groove.

'The object of this invention is to minimize noise in the reproduction of sound from disc type records, a feature of the invention belng a means for decreasing the tendency of the reproducer to leave its groove.

In general the object is accomplished by distributing the mass of the arm in such a manner as to cause its center of percussion to fall over its point of support when the stylus is taken as the axis of rotation. Vibrations at the support are thus reduced to turning movements about the stylus upon which they have little or no disturbing effect. A spring suitably mounted and tensioned is used to compensate for the lateral components of stylus friction.

1n the accompanying drawing are shown two views of a reproducer arm incorporating the novel features of this invention.

Fig. 1 is a side elevation of a reproducer with a friction compensating spring; and

Fig. 2 is a plan view of the same reproducer.

Referring now to Fig. 1, 10 is a stylus cooperating with a record 11 and actuating an electrical pickup 12. The record may be of either the lateral or hilli-and-dale type. The pickup is supported by an'arm 13 pivoted for vertical motion at 14 and for lateral mopart tion at 15. It is counter balanced for a predetermined needle pressure by a weight 16.

To obtain a center of percussion located over the pivot the mass supported by the pivot must be so distributed that where Y L is the distance from the stylus to the ivot.

I is the moment of inertia of the pivote portion about an axis through the needle.

W is the weight of the pivoted portion.

w -is the distance from the center of gravity of the pivoted portion to the needle.

9 isthe acceleration of'gravity.

Since it is difficult to make the arm so that its moment of inertia about the vertical axis is equal to its moment of inertia about the horizontal axis, L will be different in each case and will require a separate location of the vertical and horizontal pivots. In some instances however, the two can be made intersecting and for the purpose of illustration the pivots are so shown in the drawing. With the center of percussion at the pivots and the axis of rotation taken through the stylus any vibration at the pivots which would normally be communicated through the arm to the stylus becomes merely a 1'0- tating movement about the stylus and therefore leaves the stylus unafl'ected. This holds true for either vertical or horizontalvibrations.

The elimination of vibration in the arm materially reduces undesirable changes in the magnetic flux between the poles of the electromagnets and thereby makes for a quiet record and more uniform reproduction withv less tendency for a reproducer to leave its groove.

To make this invention applicable to the majority of recorders and reproducers now in use, all that is required is a suitable counterbalancing weight to give the proper location I 17 is sup by a rigr member 19 which bent to allow free movement to the weight 16 The other end of the spring is secured to the projection 20 of the arm 13. The tension in the spring.

placement. Now, the force of friction between the stylus and record hes a lateral component which always tends to turn the arm to a position such that a line drown through the stylus and vertical axis is tangent to the groove at the stylus. If the spring is so positioned that its center line intersects the pivot at the tangent position of the arm, any displacement of the arm vfrom this position will cause the spring to become eccentric to the pivot and thereby establish a turning moment which will tend to increase the displacement. The lateral component of the force of friction varies very nearly as the displacement oi the arm from the tangent position and since the eccentricity of the spring also varies as the displacement of the arm, these two forces can be made to balance one another to secure better tracking.

Referring to Fig. 2, let A represent an extreme position of the stylus. The needle friction for this osition will be some force acting tangentially to the groove. This force may be resolved into two components f acting along the center line of the arm and f acting normal to the center line'. The spring tension S acts along the center linepf the spring and for the position shown the center line will have an eccentricity E. If 6 is the angle between the tangent and end positions of the reproducer arm and L is the distsnce from the stylus to the pivot, then for equilibrium S. E.=f v sinQHZ or the spring force for any position will he can be determined by experiment and for a given machine 0 L are known. Hence the only other variables are and S. E can be assumed from the sine and shape of the arm thus making it pos ible to determine the spring tension required.

By taking moments about the pivot for ver= tics-l movement the equivalent Weight which the spring tension replaces now be determined. Since the bearing pressure of the stylus is fixed, however, any excess or loci:

orteci at one end from the base 18' essence of tension must be adjusted r'or by changing the eccentricity of the spring relative to the pivot for vertical movement.

Although the invention been described with reference to e psrticnler embodiment for the purpose of illustration, its see c is not to be limited thereby but is to he eter= mined. by the appended claims.

What is claimed is: I

. l. A. translating device for phonogrephs an arm for the transleting ivc niiy monnz'zed' v end means for reducing; vihrstions at the pivot to novements about the stylus.

2'. A translating {for gillonegrincls an arm for the trrqnsl: s device pivotslly mounted, and mess of.

predetermined size and ol stri bntion tor repivot to tzmnng cincing vibrations movements about th 3. A; SiSylIZS actuatea device for phonograph records a end means for coontembalancing the component of the force er friction the stylus and the record.

4. A stylus actuated for phone mph records. c. ceopereting with t e stylus, and e. spring tor counter-helancing the laterel component oi the force oi. the friction between the stylus and record.

5. A. stylus actuated device for phonographrecords, o cooperating with the stylus, an erro pivotslly mounted for the translating device e spring for coon ter belencing the loterel component'of the force of the i'riction between the stylus end record, said spring being positions so thet its center line passes over the ivot when the arm is in a tangent or nentro position.

6. A stylus actuated translating device for phonograph records, a type record coole crating with. the stylus. an arm pivotally mounted for the translating device, and 2 spring for connter-belencing the laterel component and the force of between the stylus and record, one end said spring being secured to the arm at some point between the pivot end stylus and the other end being held by a rigid member on the opposite side of the pivot.

7. A stylus actuated translating device for phonogrsphs a support the translating device pivotally mounted, o disc type record cooperating with the stylus eompris ing 8. mass of predetermined and distribntion for reducing vi t the pivot to turning movements the stylus and. spring means for compensating the lateral component of the force of friction between the stylus and record said spring coopersting with the mass to reduce the amount oibearing pressure on the yles.

8. A stylus actuated Eating device for phonographs, an arm f translating de vice pivotally mounted. foe record cooperating with the stylus, and a mass of predetermined weight and distribution secured to the arm such that the center of percussion of the combined translating device, arm and mass falls over the pivot when the stylus is taken as the axis of rotation.

In witness. whereof, I hereunto subscribe my name this 17th day of J my 1931.

LLOYD A. ELMIER. 

